Which of the following is $NOT$ a characteristic of the phylum $Annelida$?

Mass $M$ is divided into two parts $xM$ and $(1-x)M$. For a given separation,the value of $x$ for which the gravitational attraction between the two pieces becomes maximum is

When the margins of sepals or petals overlap one another without any particular direction,the condition is termed as

When zeolite (hydrated sodium aluminium silicate) is treated with hard water,the sodium ions are exchanged with:

$A$ constant torque acting on a uniform circular wheel changes its angular momentum from $A_0$ to $4A_0$ in $4 \ s$. The magnitude of this torque is

$\cos 36^{\circ} - \cos 72^{\circ}$ is equal to